1. Field of the Invention
The present invention relates to multimedia search. Particularly, the present invention relates to a method for setting a dominant color, where the dominant color is included as a feature for searching the multimedia data.
2. Description of the Related Art
In a traditional image search system, it suggests a method for setting a dominant color of images that the images are divided into n×m number of grids, color histograms are obtained for each divided cell, and a representative color having maximum bin of color histogram is designated as the dominant color of a particular region. In other cases, an average value of color histogram or a major hue vector is selected as the dominant color of the particular region.
To be short, the dominant color can be determined by a method of using an average color value of a given region; choosing one most frequently appeared color; choosing the n most frequently appeared colors; using a color that prevails in a designated region by more than p %, or using a histogram, and so forth.
Each method described above has relative advantages and disadvantages in its own way.
For instance, the method using histogram makes it possible to finely represent the color. However, it requires a lot of data and sometimes set the dominant color for colors occupying extremely small part of the region.
Another method taking a single average value is advantageous that it has abridged data information and is capable of performing a pre-filtering function in a content-based search. Unfortunately however, if the region is composed of a variety of colors, it is pretty hard to accurately represent the dominant color.
However, considering that the characteristics of images are usually diverse and that in most cases it is difficult to express various colors by a single color value, the method of expressing an image region using only one dominant color is rather inappropriate or insufficient to represent the entire characteristics of the images and to construct a precise image characteristic database, so that it causes a deterioration of a performance of an image search using such a characteristic database.
Moreover, a method of expressing a dominant color of a region based on a variety of colors not only occupies a lot of storage space, but also makes it difficult to precisely represent mutual relations among the colors. In many cases, it is also hard to determine the dominant color based on a color distribution of a given image region, and the dominant color value obtained by this method lacks precision.
Taking all the aforementioned problems into consideration, inventors of the present inventions introduced a new method for describing color information of a given image region, in which the image region is represented by several dominant colors and their frequencies (ratio of the dominant colors in a given region, percentage %), a spatial coherency (it is called as a ‘reliability’) for the dominant colors is defined, and such a reliability is used for the image search together with the dominant colors to improve performance of the image search. This method is described in Korean Patent Application No. 1999-3181 (corresponding to U.S. patent application Ser. No. 09/479,888 filed on Jan. 10, 2000 and PCT Application No. PCT/KR99/00849 filed on Dec. 31, 1999) and Korean Patent Application No. 1999-26784 (corresponding to U.S. patent application Ser. No. 09/609,392 and PCT Application No. PCT/KR00/00710, both filed on Jul. 3, 2000.
Here, the spatial coherency can be a clue or information how much the dominant colors of the given image region are reliable, and it also indicates how densely the dominant colors are mixed together in the image region.
Therefore, when the spatial coherency is defined together with the dominant color, one can find out how reliable the dominant color thereof is at the time of the image search, and based on this, more improved search can be realized.
As a result, it is concluded that performance of the image search is greatly influenced by how precisely the spatial coherency represents the reliability of the dominant color.
Therefore, it is evident that a simple uniform quantization of the spatial coherency is not sufficient to reflect the diverse characteristics of the images. Thus, a more improved quantization scheme of the spatial coherency is required.